The present disclosure relates to power distribution systems. More particularly, the present disclosure relates to energy calculation methods in power distribution systems.
Industrial power distribution systems commonly divide incoming power into a number of branch circuits. The branch circuits supply power to various equipment (i.e., loads) in the industrial facility. Circuit breakers are typically provided in each branch circuit to facilitate protecting equipment within the branch circuit. Circuit breakers are designed to open and close a circuit by non-automatic means and to open the circuit automatically on a predetermined over-current without damage to itself when properly applied within its rating. The circuit breakers commonly include protective elements enclosed within the body of the circuit breaker. One common type of protective element is known as an electronic trip unit. The circuit breaker and its protective element have proven useful at managing the protection of the loads on the circuit.
However, it can be desired to integrate the load management of the branch circuits to one another. Further, it can be desired to integrate the management of the loads on the branch circuits with the management of the power sources feeding the branch circuits. Still further, it can be desired to provide for energy calculations of the circuits within the system, where such energy calculations require both current and voltage inputs.
In order to provide this integrated protection and monitoring, prior distribution systems have required costly and difficult to implement solutions. Today, each of these functions is performed by separate hardware often with separate sensors necessary to measure system parameters and auxiliary devices in power circuit interrupters to switch the power circuits. In such prior systems, hard wire connections between all of the electronic trip units in the system was required in order to coordinate the load control decisions of each independent trip unit with the other trip units in the system. Further, hard wire connections were also required to provide information for the independent electronic trip units to the separate system performing feed management decisions. The control decisions by the separate system performing feed management decisions is made more complex because the information from the various independent electronic trip unit is typically out of phase with one another. Additionally, another hardware device is required to then provide the desired monitoring functionality.
In order to provide the desired energy calculations, some prior power distribution systems have required each breaker to have its own dedicated current transformer for current sensing and potential transformer for sensing voltage. Some prior systems have required each breaker to have its own current transformer but received the required voltage sensing from a potential transformer that was shared among two or more breakers. However, these prior systems required dedicated wiring from each circuit breaker to the shared potential transformer.
Accordingly, there is a continuing need for power distribution systems having methods of performing energy calculations in an economical, flexible, and programmable manner.